Something I've struggled with for ages is when is it applicable to uber to save players and/or position and when is it better to back out and preserve uber?

More often than not I find myself ubering to save my pocket or demo whilst the enemy has 3 or more enemy players attacking us when they have player ad, We stay in and attack to try and get frags with the uber, And if the gamble fails we end up being overrun by their player ad.

So I was hoping to get some general advice on when I should be ubering. And when it's best to just fall back and hold with uber + respawners

No Mercy

It's pretty situational and often comes down to playstyle of your soldier and/or demo. If your soldier is aggressively minded (myself for example), they might often like to aggressively uber in an attempt to get kills and at the very least, buy time for respawns so you can still hold that forward position. You need to do it in an area where 1) they wont get juggled easily, 2) it's easy for you to chase and 3) escape isn't difficult for your team.

A good example is ubering demo + sold around badlands choke - your demoman can chase them into their house with a tick of uber while your soldier chases rocketjumping wildly as well. You a) can't get juggled easily there, b) it's easy for your team to chase and c) you have 2 escape routes (3 if you include valley) if things go poorly.

I guess it also depends on times for respawns. If your players have 10-15 second respawns it's probably not ideal to commit to something like that.

No Mercy

Every situation is different, and the position and uber nature of your opposing medic is a deciding factor.

If both teams have uber and their medic is within range looking to pop uber, but ideally 2nd, It is worth saving any player from dying and trust him to force the opposing uber pop within 1-2 seconds and just ride out the slight disadavantage (think about where to be safe post uber assuming the multis are even).

If alternatively they are applying strong spam pressure or suiciding with their medic out of sight, or even you are attempting to push and they are far back then as a rule of thumb i am happy to let the first heavy die, but not the second. Dont go below 4 players or 2 play disadvantage

In the exact situation you are describing one things stand out to me:
Sometimes this is correct, but sometimes it is unrealistic to expect many kills from and the uber, or it is fine to hold with players and uber disadvantage. Regardless of the nature of the uber, always have a smart and safe post uber exit strategy, certianly for your self and sometimes for the ubered player (though sometime he will have to jump in suicide to get the much needed high risk equalizing kill or uber pop). Know when you need to cash in the bad uber pop and all just retreat and prepare for a safer defense further back.

'Desperation' uber pops with play disavantage work better in enclosed areas, which is why it is often done by choice in granary 2nd point to trade ubers and buy time for respawns. The intent is usually not to be agressive but to use uber to buy time and restore equality.

As always ubers will be much more successful if the primary is aware to expect it and prepare for counter aggression.

No Mercy

Oh I kind of misread it - your players shouldn't be taking so much damage that you have to uber to save them from spam. But if you have to it's probably for the best (VERY SITUATIONAL DOESN'T APPLY ALL THE TIME). It sucks to have player disadvantage - I'd prefer uber disadvantage over player disadvantage personally.

No Mercy

some situations with player disadvantage you can do an aggressive uber on the point to buy time for respawners to come in and fight (so defending badlands middle you set it up so the soldier medic are in house and as the other team are capping you go into them) part of the problem like bowt said is no one on your team is probably thinking that

if you are still dying after the uber you just have to try and read that you are losing the fight and get out so you can defend

another situation might be attacking granary last with some player advantage, your players force them to use uber but some of them are going to die, instead of trying to save them its a better move to get out with your demoman / anyone else so that you can defend and have uber advantage